Enclosure structure system for deep foundation pit engineering and construction method thereof

Abstract

The invention provides an enclosure structure system for deep foundation pit engineering and a construction method of the enclosure structure system. The system comprises a vertical water interception supporting unit, an inclined bottom expanding supporting unit and a permanent support changing transition unit which cooperatively form an integrated structure. The vertical water interception supporting unit is an HC combined pile wall, the inclined bottom-expanding supporting unit is a bottom-expanding inclined supporting pile with a bell-jar-shaped expanding head, and the permanent support changing transition unit comprises a water stop wing ring and a support changing plate strip. During construction, the HC combined pile wall is firstly constructed, then the expanded-base diagonal bracing piles are arranged, and finally load conversion is achieved through the water stop wing rings and the support changing plate strips. Through an integrated structure combination and a systematized construction process, collaborative operation of vertical water interception supporting, inclined bottom expanding supporting and permanent supporting changing conversion is achieved, and the problems that in the prior art, a supporting system is complex, the collaboration is poor, passive area reinforcement is poor, and the integrity of the system is insufficient are solved; the method is suitable for construction projects such as high-rise building basements, underground comprehensive pipe galleries, large underground parking lots and commercial spaces.

Description

Technical Field

[0001] This invention relates to the fields of geotechnical engineering and underground construction engineering, and in particular to a retaining structure system and its construction method for deep foundation pit engineering. Background Technology

[0002] In deep foundation pit engineering, the retaining structure must simultaneously bear the core functions of soil retention and water stoppage. Current mainstream retaining structures include diaphragm walls, bored pile banks, steel-cement-soil mixing walls (such as SMW method piles), and HC method piles. Among these, the HC method pile, which embeds high-strength steel into a continuous cement-soil mixing wall to form a composite wall that combines soil retention, water stoppage, and a certain degree of rigidity support, is becoming increasingly widely used.

[0003] To resist lateral water and soil pressure after foundation pit excavation and control wall deformation, existing technologies mainly employ three types of solutions: 1. Conventional internal bracing combined with HC pile scheme: HC piles are used as retaining walls, with multiple horizontal concrete or steel supports. However, HC piles have limited bending resistance, and deep foundation pits require multiple layers of horizontal support, leading to frequent overlap of construction procedures, time-consuming concrete support curing, and complex steel support node design. This not only prolongs the construction period but also increases material costs and construction waste. Dense support further restricts the working space and efficiency within the pit.

[0004] 2. Inclined bracing piles as a partial alternative to internal bracing: In pile foundations or diaphragm wall retaining pits, inclined bracing piles are used locally to replace horizontal supports to create open working space. However, when inclined bracing piles are simply combined with flexible HC method piles, the rigidity / hinged state of the connection nodes is difficult to control precisely. Mismatched stiffness, weak connection structure, or improper installation timing can lead to inefficient load transfer, premature wall deformation, and secondary bending moments generated by the inclined bracing piles, resulting in poor deformation control and potential safety hazards.

[0005] 3. Combined HC pile and passive zone reinforcement scheme: Relying on the inherent stiffness of the HC piles, the passive zone soil at the bottom of the foundation pit is reinforced (e.g., cement-soil mixing) to enhance resistance. However, large-scale deep soil reinforcement involves a large workload, high cost, and long construction period. Construction is prone to disturbing the surrounding soil, and the strength and modulus of the reinforced soil are uneven. Long-term performance is affected by groundwater, resulting in high uncertainty in passive resistance. Conservative design values ​​further increase costs.

[0006] The core flaw of the above scheme is that it fails to organically integrate the continuous water-stopping and bending resistance characteristics of HC method piles with the axial pressure transmission advantages of inclined bracing piles through an integrated structure. The retaining structure and the supporting structure are mostly designed independently and then simply assembled, resulting in insufficient coordination. It is difficult to balance economy, construction efficiency and deformation control accuracy, and cannot meet the comprehensive needs of deep and large foundation pit projects in complex urban environments. Summary of the Invention

[0007] To address the aforementioned problems, this invention provides a retaining structure system and its construction method for deep foundation pit engineering. It is applicable to construction projects such as basements of high-rise buildings, urban subway stations, underground integrated pipe corridors, large underground parking lots, and commercial spaces. It is particularly suitable for deep foundation pit support scenarios in complex surrounding environments in urban built-up areas, and can achieve soil stability assurance, precise deformation control, and effective protection of adjacent buildings and underground pipelines.

[0008] To solve the above problems, the technical solution adopted by the present invention is as follows: A retaining structure system for deep foundation pit engineering includes a vertical water-cutting support unit, an inclined bottom expansion support unit, and a permanent replacement support transition unit, which work together to form an integrated retaining system. The vertical water-cutting support unit is a continuous HC composite pile wall, which consists of a cement-soil mixing wall, alternately implanted H-beams and Larssen sheet piles, and a reinforced concrete top ring beam at the top of the piles. The top ring beam is equipped with corbels. The inclined base support unit consists of several inclined base bracing piles. The ends of the inclined base bracing piles are provided with bell-shaped enlarged heads, and the top ends are connected to the corbels of the top ring beam through high-strength cast steel hinged supports. The permanent replacement support transition unit includes a water-stop wing ring and a replacement support plate strip. The water-stop wing ring is an L-shaped reinforced concrete component. The horizontal part is integrally cast with the basement floor slab, and the vertical part is closely attached to the HC composite pile wall and welded to the steel plate water-stop strip pre-embedded in the construction joint of the floor slab. The replacement support plate strip is a reinforced reinforced concrete plate strip.

[0009] Preferably, in the vertical water-cutting support unit, the pile diameter of the cement-soil mixing wall is 850mm, and the overlap length of adjacent piles is 250mm.

[0010] Preferably, the H-beam has the specifications of H500×300×11×18, and the Larssen sheet pile has the specifications of SP-IV and a width of 400mm.

[0011] Preferably, the cross-sectional dimensions of the top ring beam are not less than 800mm×600mm, the main reinforcement is configured as no less than 8 steel bars with a diameter of 22mm, and the stirrups are spiral stirrups with a diameter of 14mm and a spacing of 100mm.

[0012] Preferably, in the inclined base support unit, the angle between the axis of the inclined base support pile and the horizontal plane is 35°-45°, the diameter of the bell-shaped enlarged head is 1.2m, and the pile spacing of the inclined base support piles is 4-6m.

[0013] Preferably, the steel pile of the expanded-base inclined bracing pile is a seamless steel pipe with a diameter of 325mm and a wall thickness of 10mm, and the outer side of the pile body is provided with spiral blades with a spacing of 500mm, a height of 150mm and a thickness of 10mm.

[0014] Preferably, the steel plate waterstop is 3mm thick and 300mm wide, and the replacement support plate is 2-3m wide and has the same thickness as the corresponding floor slab.

[0015] The present invention also provides a construction method based on the enclosure structure system according to any one of claims 1-7, characterized by comprising the following steps: Step 1: Construction of Vertical Water Interception Support Unit: a. Measurement and layout: Accurately lay out the edge line of the foundation pit and the center axis of the HC combined pile wall, with the pile position deviation controlled within ±20mm; b. Excavation of the guide trench and setting of positioning steel: Excavate a guide trench with a width of about 1.0m and a depth of 1.5m along the axis of the pile wall, and set H-beams vertically as positioning and guiding references, with a verticality deviation of less than 1 / 300; c. Construction of mixing piles: A three-axis cement-soil mixing pile machine with a motor power of ≥90kW is used to cut and mix the soil along the axis. The mixing blades descend at a speed of 25-30rpm and rise at a speed of 35-40rpm. Cement grout with a water-cement ratio of 1.2-1.5 is injected at a grouting pressure of 0.81-1.2MPa. The cement content per cubic meter of soil is ≥20%, forming a continuous cement-soil mixing wall. H-beams and Larssen sheet piles combined for implantation: Within 30 minutes after pile formation, heavy hydraulic vibratory hammers are used to alternately and vertically implant H-beams and Larssen sheet piles, with an implantation verticality of less than 1 / 250. e. Construction of the top ring beam: Pour reinforced concrete top ring beam to form an integral load-bearing foundation; Step Two: Construction of the Inclined Expansion Base Support Unit: a. Preliminary excavation of the foundation pit: Excavate to a working surface 3-5m below the ground and monitor the displacement of the HC combined pile wall; b. Positioning and construction of inclined bracing piles: Lay out the position and inclination direction of the pile core, use an integrated inclined pile machine for construction, and simultaneously pour cement grout into the steel piles to form straight holes and bell-shaped enlarged heads; c. Node connection: The top of the expanded-base inclined brace pile is connected to the corbel of the top ring beam by a high-strength cast steel hinged support; Step 3: Construction and stress transfer of the permanent support transition unit: a. Subsequent excavation of the foundation pit: After the expanded bottom inclined support piles reach the design strength, the remaining soil is excavated over a large area; b. Construction of water-stop wing ring: When pouring the basement floor slab, the L-shaped water-stop wing ring is poured simultaneously and welded to the steel plate water-stop strip for connection; c. Construction of replacement support strip: When pouring the basement floor slab, construct the replacement support strip; d. Stress conversion and removal: After the concrete strength of the replacement support plate and adjacent structures reaches 100% of the design value, the prestress of the expanded-base inclined support piles is released in stages. After monitoring and finding no abnormalities, the pile heads are cut off and the H-beams and Larssen sheet piles are recovered.

[0016] In step one c, the compressive strength of the cement grout is not less than 10 MPa after 7 days of standard curing and not less than 15 MPa after 28 days; in step two b, the water-cement ratio of the cement grout injected simultaneously during steel pile driving is 1.2-1.5, and the grouting pressure is 0.8-1.0 MPa.

[0017] In step 1d, the excitation force of the heavy hydraulic vibratory hammer is 150-200kN, and the implantation speed is controlled at 0.5-1.0m / min; in step 3c, the shear keyway depth of the support plate is 50-80mm, the width is 100-150mm, and the spacing between adjacent keyways is 300-500mm.

[0018] The beneficial effects of this invention are as follows: 1. The combination of H-beams and Larssen sheet piles significantly improves the bending stiffness (EI) of the cement-soil mixing wall. The enlarged-base inclined bracing piles, through high-strength cast steel hinged supports, convert the lateral displacement of the HC composite pile wall into its own axial pressure, resulting in extremely high mechanical efficiency. Under the same geological conditions and foundation pit depth, the maximum lateral displacement is significantly lower than that of traditional multi-level horizontal support systems, effectively reducing adverse impacts on adjacent buildings, subway tunnels, important pipelines, and other sensitive facilities, thus meeting the stringent environmental protection requirements of urban core areas.

[0019] 2. Expanded-base inclined bracing piles replace most or even all of the horizontal internal supports, avoiding the cyclical operation of "layered excavation and layer-by-layer support". Earthwork excavation can be carried out on a large scale at one time, significantly improving construction efficiency. The expanded-base process increases the bearing capacity of a single pile, which can reduce the total number of inclined bracing piles. At the same time, it saves a lot of raw materials, manufacturing, installation and dismantling costs of horizontal supports. The unsupported open space improves the efficiency of mechanical operations, reduces labor costs, and the overall cost is lower than that of traditional internal support schemes.

[0020] 3. The bell-shaped enlarged head and helical blades of the expanded-base inclined bracing pile work together to completely eliminate the risk of pull-out failure on the pile body; the high-strength cast steel hinged support ensures clear stress at the nodes, making the structural calculation model highly consistent with the actual stress state; the permanent transition structure of "water-stop wing ring + replacement support plate" realizes the smooth transfer of temporary support load to the permanent structure, avoids stress concentration and sudden changes, prevents accelerated deformation of the wall during the stress transition period, and ensures the long-term safety of the foundation pit and basement construction.

[0021] 4. The water-stop wing ring and the replacement support plate are not only functional structures but also components of the permanent main structure, optimizing the stress state of the permanent structure; the H-beams and Larssen sheet piles in the HC composite pile can be safely recycled, reducing steel resource consumption and construction waste, which meets the requirements of green construction and sustainable development; the open working space improves ventilation and lighting conditions in the pit, increases the efficiency of large machinery operations, and reduces the safety risks of workers working at heights and in confined spaces. Attached Figure Description

[0022] Figure 1 This is a schematic diagram of the overall structure of the enclosure structure system of the present invention; Figure 2 This is a schematic diagram of the connection structure between the expanded-base inclined bracing pile and the top ring beam of the present invention.

[0023] In the diagram: 1 HC composite pile wall, 2 enlarged bottom inclined bracing pile, 3 top ring beam, 4 waterstop wing ring, 5 replacement support plate belt, 6 H-beam, 7 Larssen sheet pile, 8 cement-soil mixing wall, 9 high-strength cast steel hinged support, 10 bell-shaped enlarged head, 11 steel plate waterstop belt, 12 spiral blade. Detailed Implementation

[0024] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Many specific details are set forth in the following description to provide a thorough understanding of the present invention. However, the present invention can be practiced in many other ways different from those described herein, and those skilled in the art can make similar modifications without departing from the spirit of the present invention. Therefore, the present invention is not limited to the specific embodiments disclosed below.

[0025] Reference Figure 1-2 A retaining structure system for deep foundation pit engineering includes a vertical water-cutting support unit, an inclined bottom-expanding support unit, and a permanent replacement support transition unit, which work together to form an integrated retaining system. Vertical water-cutting support unit: It is a continuous HC composite pile wall 1, which serves as the main body for soil retention and water stoppage during the foundation pit excavation stage. It consists of cement-soil mixing wall 8, alternately implanted H-beams 6 and Larssen sheet piles 7, and a reinforced concrete top ring beam 3 at the top of the piles. The top ring beam 3 is equipped with corbels for connecting with the inclined bottom expansion support unit. The H-beams 6 and Larssen sheet piles 7 are implanted into the cement-soil mixing wall 8 at intervals of "one H-beam and one sheet pile" or "one H-beam and two sheets piles" to form a continuous load-bearing whole.

[0026] Inclined base support unit: Composed of several inclined base bracing piles 2, used to bear the main horizontal load and realize axial transmission; the pile end of the inclined base bracing pile 2 is provided with a bell-shaped enlarged head 10, and the top end is connected to the corbel of the top ring beam 3 through a high-strength cast steel hinged support 9. The hinged joint ensures that the load is transmitted only along the axial direction, avoiding the generation of secondary bending moment.

[0027] The permanent replacement support transition unit includes a water-stop wing ring 4 and a replacement support plate 5, which are used to achieve a permanent transfer of the force of the support system. The water-stop wing ring 4 is an L-shaped reinforced concrete component. The horizontal part is integrally cast with the basement floor slab, and the vertical part is closely attached to the HC composite pile wall 1. It is also welded to the steel plate water-stop 11 pre-embedded in the construction joint of the floor slab to form a double water-stop and force transmission structure. The replacement support plate 5 is a reinforced concrete plate slab close to the retaining wall. The reinforcement ratio is more than 50% higher than that of ordinary floor slabs, and shear keyways are added to enhance the force transmission stability.

[0028] Furthermore, the cement-soil mixing wall 8 has a pile diameter of 850mm and an overlap length of 250mm between adjacent piles to ensure continuous water-stopping; the H-beam 6 has a specification of H500×300×11×18, and the Larssen sheet pile 7 has a specification of SP-IV and a width of 400mm, taking into account both bending and shear resistance.

[0029] The cross-sectional dimensions of the top ring beam 3 are not less than 800mm×600mm. The main reinforcement is configured as no less than 8 steel bars with a diameter of 22mm, and the stirrups are spiral stirrups with a diameter of 14mm and a spacing of 100mm, to ensure overall rigidity and connection reliability.

[0030] The angle between the axis of the expanded-base inclined bracing pile 2 and the horizontal plane is 35°-45°, preferably 40°. The diameter of the bell-shaped enlarged head 10 is 1.2m. The pile spacing of the expanded-base inclined bracing pile 2 is 4-6m, and the arrangement is optimized according to the bending moment distribution of the HC combined pile wall 1. The steel piles of the expanded-base inclined bracing pile 2 are made of seamless steel pipes with a diameter of 325mm and a wall thickness of 10mm. The outer side of the pile body is provided with spiral blades 12 with a spacing of 500mm, a height of 150mm, and a thickness of 10mm to improve the pull-out resistance and bearing capacity of the pile body.

[0031] The steel plate waterstop 11 is 3mm thick and 300mm wide to ensure the water-stopping effect of the construction joint; the replacement support plate 5 is 2-3m wide and the thickness is consistent with the corresponding floor slab, adapting to different structural floor height requirements.

[0032] A construction method for a retaining structure system for deep foundation pit engineering includes the following steps: 1. Construction of vertical water interception support unit (support stage) Measurement and layout: According to the design drawings, accurately lay out the edge line of the foundation pit and the center axis of HC combined pile wall 1, and control the pile position deviation within ±20mm to ensure the position accuracy of the wall.

[0033] Excavation of guide trench and setting of positioning steel: Excavate a guide trench about 1.0m wide and 1.5m deep along the axis of the pile wall. After removing debris from the bottom of the trench, set H-beams vertically as positioning and guiding reference. The verticality deviation is less than 1 / 300 to ensure the accuracy of subsequent wall construction.

[0034] Construction of mixing piles: A three-axis cement-soil mixing pile machine with a motor power of ≥90kW is used to cut and mix the soil in situ along the axis; the mixing blades descend at a speed of 25-30rpm and rise at a speed of 35-40rpm; during the mixing process, cement slurry with a water-cement ratio of 1.2-1.5 is sprayed in, with a grouting pressure of 0.8-1.2MPa, and the cement content per cubic meter of mixed soil is ≥20%, forming a continuous and seamless cement-soil mixing wall. The compressive strength of the cement slurry is not less than 10MPa after 7 days of standard curing and not less than 15MPa after 28 days, ensuring the strength of the wall and its water-stopping performance.

[0035] H-beams and Larssen sheet piles are implanted together: Within 30 minutes after pile formation (before the initial setting of cement and soil), a heavy hydraulic vibratory hammer with an excitation force of 150-200kN is used to alternately and vertically implant H-beams 6 and Larssen sheet piles 7 into the mixing pile body. The implantation speed is controlled at 0.5-1.0m / min, and the verticality of implantation is less than 1 / 250 to ensure the effectiveness of the component in bearing the force.

[0036] Construction of the top ring beam: After all HC composite piles are completed, tie the steel bars of the top ring beam 3 (no less than 8 main bars with a diameter of 22mm, stirrups with a diameter of 14mm and a spacing of 100mm), pour concrete to form the top ring beam 3 with a cross section of not less than 800mm×600mm, add corbels as the upper end of the inclined support piles to connect the foundation, and cure to the design strength before proceeding to the next process.

[0037] 2. Construction of the inclined base support unit (in the stage of inclined bracing loading) Preliminary excavation and working face preparation of the foundation pit: Excavate the foundation pit to 3-5m below the ground (design elevation of the inclined support pile) to form a flat construction working face. During the excavation process, use an inclinometer to monitor the displacement of HC combined pile wall 1 to ensure the stability of the wall.

[0038] Positioning and construction of inclined bracing piles: Based on the design drawings and the bending moment distribution diagram of HC combined pile wall 1, the pile core position and inclination direction (angle 35°-45°, preferably 40°) of the enlarged base inclined bracing pile 2 are laid out. The inclined pile integrated machine is used for construction. During the pile driving process of steel pile (325mm diameter, 10mm wall thickness seamless steel pipe), cement grout (water-cement ratio 1.2-1.5, grouting pressure 0.8-1.0MPa) is injected simultaneously. The straight hole drilling and the formation of the 1.2m diameter bell-shaped enlarged head 10 are completed in one go. Spiral blades 12 with a spacing of 500mm, a height of 150mm, and a thickness of 10mm are set on the outside of the pile body to improve the bearing capacity of the pile body.

[0039] Node connection: The top of the expanded-base inclined brace pile 2 is connected to the corbel of the top ring beam 3 through a high-strength cast steel hinged support 9 to ensure that the node only transmits axial force and avoids complex bending moment transmission.

[0040] 3. Construction and stress conversion of permanent support transition unit (support conversion stage) Subsequent excavation of the foundation pit: After the expansion base inclined support pile 2 reaches the design strength, large machinery will be used to carry out large-scale excavation of the remaining soil in the foundation pit in the open space without horizontal support, thereby improving construction efficiency.

[0041] Construction of "water-stop wing ring": When pouring the basement floor slab (usually the B1 floor slab), a 3mm thick and 300mm wide ring-shaped steel plate water-stop 11 is pre-embedded at the construction joint of the floor slab. At the same time, an L-shaped reinforced concrete water-stop wing ring 4 is poured, so that its horizontal part is poured as a whole with the floor slab, and its vertical part is closely attached to the HC composite pile wall 1 and welded to the steel plate water-stop 11 to form a rigid water-stop and force transmission transition structure.

[0042] Construction of "Replacement Support Strip": When pouring the floor slabs of each basement floor (especially the top slab of B1 floor), a replacement support strip 5 is constructed near the retaining wall. The replacement support strip 5 is 2-3m wide and the thickness is the same as the floor slab of the corresponding floor. The reinforcement ratio is increased by more than 50% compared with ordinary floor slabs. Shear keyways with a depth of 50-80mm, a width of 100-150mm, and an adjacent spacing of 300-500mm are added to enhance the reliability of force transmission.

[0043] Force conversion and temporary component removal: After the concrete of the replacement support plate 5 and the adjacent structure has been cured for 28 days and the strength reaches 100% of the design value, the prestressed locking devices on the expanded-base inclined bracing piles 2 are released in stages and symmetrically. After each release, the deformation of the HC combined pile wall 1 is monitored. After no abnormal growth is found, the upper pile head of the expanded-base inclined bracing piles 2 is cut off, and the H-beam 6 and Larssen sheet piles 7 are safely recovered (if designed to be recyclable), thus completing the force conversion from the temporary support system to the permanent structure.

[0044] It is suitable for construction projects such as basements of high-rise buildings, urban subway stations, underground integrated pipe corridors, large underground parking lots and commercial spaces. It is especially suitable for deep foundation pit support scenarios in complex surrounding environments in urban built-up areas, and can achieve soil stability protection, precise deformation control and effective protection of adjacent buildings and underground pipelines.

[0045] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A retaining structure system for deep foundation pit engineering, characterized in that, It includes vertical water-cutting support units, inclined bottom expansion support units, and permanent replacement support transition units, which work together to form an integrated retaining system; The vertical water interception support unit is a continuous HC composite pile wall (1), which consists of a cement-soil mixing wall (8), alternately implanted H-beams (6) and Larssen sheet piles (7), and a reinforced concrete top ring beam (3) at the top of the piles. The top ring beam (3) is equipped with corbels. The inclined base support unit consists of several inclined base bracing piles (2). The pile end of the inclined base bracing pile (2) is provided with a bell-shaped enlarged head (10), and the top end is connected to the corbel of the top ring beam (3) through a high-strength cast steel hinged support (9). The permanent replacement support transition unit includes a water-stop wing ring (4) and a replacement support plate (5). The water-stop wing ring (4) is an L-shaped reinforced concrete component. The horizontal part is integrally cast with the basement floor slab, and the vertical part is closely attached to the HC composite pile wall (1) and welded to the steel plate water-stop strip (11) pre-embedded in the construction joint of the floor slab. The replacement support plate (5) is a reinforced concrete plate strip.

2. The retaining structure system for deep foundation pit engineering according to claim 1, characterized in that, In the vertical water interception support unit, the pile diameter of the cement-soil mixing wall (8) is 850mm, and the overlap length of adjacent piles is 250mm.

3. The retaining structure system for deep foundation pit engineering according to claim 1, characterized in that, The H-beam (6) has a specification of H500×300×11×18, and the Larsen sheet pile (7) has a specification of SP-IV and a width of 400mm.

4. The retaining structure system for deep foundation pit engineering according to claim 1, characterized in that, The cross-sectional dimensions of the top ring beam (3) are not less than 800mm×600mm, and its main reinforcement is configured as no less than 8 steel bars with a diameter of 22mm, and the stirrups are spiral stirrups with a diameter of 14mm and a spacing of 100mm.

5. The retaining structure system for deep foundation pit engineering according to claim 1, characterized in that, In the inclined base support unit, the angle between the axis of the inclined base support pile (2) and the horizontal plane is 35°-45°, the diameter of the bell-shaped enlarged head (10) is 1.2m, and the pile spacing of the inclined base support pile (2) is 4-6m.

6. The retaining structure system for deep foundation pit engineering according to claim 1, characterized in that, The steel pile of the expanded base inclined support pile (2) is made of seamless steel pipe with a diameter of 325mm and a wall thickness of 10mm. The outer side of the pile body is provided with spiral blades (12) with a spacing of 500mm, a height of 150mm and a thickness of 10mm.

7. The retaining structure system for deep foundation pit engineering according to claim 1, characterized in that, The steel plate waterstop (11) is 3mm thick and 300mm wide, and the replacement support plate (5) is 2-3m wide and has the same thickness as the corresponding floor slab.

8. A construction method based on the enclosure structure system according to any one of claims 1-7, characterized in that, Includes the following steps: Step 1: Construction of Vertical Water Interception Support Unit: a. Measurement and layout: Accurately lay out the edge line of the foundation pit and the center axis of the HC combined pile wall (1), and control the pile position deviation within ±20mm; b. Excavation of the guide trench and setting of positioning steel: Excavate a guide trench with a width of about 1.0m and a depth of 1.5m along the axis of the pile wall, and set H-beams vertically as positioning and guiding references, with a verticality deviation of less than 1 / 300; c. Construction of mixing piles: A three-axis cement-soil mixing pile machine with a motor power of ≥90kW is used to cut and mix the soil along the axis. The mixing blades sink at a speed of 25-30rpm and lift at a speed of 35-40rpm. Cement grout with a water-cement ratio of 1.2-1.5 is injected at a grouting pressure of 0.81-1.2MPa. The cement content per cubic meter of soil is ≥20%, forming a continuous cement-soil mixing wall (8). H-shaped steel and Larssen sheet pile combination implantation: Within 30 minutes after pile formation, heavy hydraulic vibratory hammer is used to alternately and vertically implant H-shaped steel (6) and Larssen sheet pile (7), with an implantation verticality of less than 1 / 250; e. Construction of the top ring beam: Pour a reinforced concrete top ring beam (3) to form an integral load-bearing foundation; Step Two: Construction of the Inclined Expansion Base Support Unit: a. Preliminary excavation of the foundation pit: Excavate to a working surface 3-5m below the ground and monitor the displacement of the HC combined pile wall (1); b. Positioning and construction of inclined support piles: Layout the position and inclination direction of the pile core, use an integrated inclined pile machine for construction, pour cement grout simultaneously with the steel pile driving, and form straight holes and bell-shaped enlarged heads (10). c. Node connection: The top of the expanded bottom inclined brace pile (2) is connected to the corbel of the top ring beam (3) by a high-strength cast steel hinged support (9); Step 3: Construction and stress transfer of the permanent support transition unit: a. Subsequent excavation of the foundation pit: After the expansion of the bottom inclined support piles (2) reaches the design strength, the remaining soil is excavated over a large area; b. Construction of water-stop wing ring: When pouring the basement floor slab, pour the L-shaped water-stop wing ring (4) simultaneously and weld it to the steel plate water-stop strip (11); c. Construction of replacement support strip: When pouring the basement floor slab, construct the replacement support strip (5); d. Force conversion and removal: After the concrete strength of the replacement support plate (5) and adjacent structures reaches 100% of the design value, the prestress of the expanded bottom inclined support pile (2) is released step by step. After monitoring for any abnormalities, the pile head is cut off and the H-beam (6) and Larssen sheet pile (7) are recovered.

9. The construction method of the enclosure structure system according to claim 8, characterized in that, In step 1c, the compressive strength of the cement grout is not less than 10MPa after 7 days of standard curing and not less than 15MPa after 28 days; in step 2b, the water-cement ratio of the cement grout injected simultaneously during steel pile driving is 1.2-1.5, and the grouting pressure is 0.8-1.0MPa.

10. The construction method of the enclosure structure system according to claim 8, characterized in that, In step 1d, the excitation force of the heavy hydraulic vibratory hammer is 150-200kN, and the implantation speed is controlled at 0.5-1.0m / min; in step 3c, the shear keyway depth of the replacement support plate (5) is 50-80mm, the width is 100-150mm, and the spacing between adjacent keyways is 300-500mm.

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